1. Field of the Invention
This invention relates to dynamic random access memories, and more particularly, to refresh counters.
2. Description of the Prior Art
Static random access memories have always been popular because of their ease of use. Dynamic random access memories, however, offer lower costs primarily because of the smaller chip area required. One of the design goals in constructing a dynamic random access memory is to maintain the internal efficiency of a dynamic RAM, while making the part look static from an external point of view. However, static RAMs require no refresh and an external refresh for a dynamic RAM would not satisfy the design objective. Therefore it is highly desirable to reduce the difficulty of refresh by including as much of the refresh circuitry as possible on chip.
Possible methods of achieving this include a separate refresh counter in the memory to keep track of refresh addresses. In this manner the counter could be incremented at the end of each refresh cycle. A further method would be the inclusion of a shift register or ring counter which would cycle through each of the word lines in a succession. However, this method, just as the first method, would require a considerable amount of additional circuitry and additional chip area. This additional area to make the part look static only serves to decrease the price gap between static and dynamic memories.